When Ford replaced Nixon(resignation) moving from VP to President, he nominated Rockefeller to be VP. The House had to approve the nomination of Rockefeller.
Oh I know...history’s my thing. In the Watergate era they had plenty of time to see it coming.
What we have now, apparently, is a batch of bad poll numbers for Biden and Harris. Plus his obvious physical decline. That doesn’t seem like enough to make the Congressional hive buzz about a potential veep. Even if they got the scuttlebutt that Biden might step down...who in Congress believes Biden? ;)
But if it did happen, Harris would think long and hard about her veep choice. Consult everyone, Dems in Congress especially. Such talk cannot have happened yet.